Many different kinds of lightweight armor systems are known and are currently being used in a wide range of applications, including, for example, aircraft, light armored vehicles, and body armor systems, wherein it is desirable to provide protection against bullets and other projectiles. While early armor systems tended to rely on a single layer of a hard and brittle material, such as a ceramic material, it was soon realized that the effectiveness of the armor system could be improved considerably if the ceramic material were affixed to or “backed up” with an energy absorbing material, such as high strength Kevlar fibers. The presence of the energy absorbing backup layer tends to reduce the spallation caused by impact of the projectile with the ceramic material or “impact layer” of the armor system, thereby reducing the damage caused by the projectile impact. Testing has demonstrated that such multi-layer armor systems tend to stop projectiles at higher velocities than do the ceramic materials when utilized without the backup layer. While such multi-layer armoring systems are being used with some degree of success, they are not without their problems. For example, difficulties are often encountered in creating a multi-layered material structure having both sufficient mechanical strength as well as sufficient bond strength at the layer interfaces.
Partly in an effort to solve the foregoing problems, armor systems have been developed in which a “graded” ceramic material having a gradually increasing dynamic tensile strength and energy absorbing capacity is sandwiched between the impact layer and the backup layer. An example of such an armor system is disclosed in U.S. Pat. No. 3,633,520 issued to Stiglich and entitled “Gradient Armor System,” which is incorporated herein by reference for all that it discloses. The armor system disclosed in the foregoing patent comprises a ceramic impact layer that is backed by an energy absorbing ceramic matrix having a gradient of fine metallic particles dispersed therein in an amount from about 0% commencing at the front or impact surface of the armor system to about 0.5 to 50% by volume at the backup material. The armor system may be fabricated by positioning successive layers of powder mixtures comprising the appropriate volume ratios of ceramic and metallic materials in a graphite die and onto a graphite bottom plunger. A top plunger is placed in the die in contact with the powder layers and the entire assembly is thereafter placed within an induction coil. Power is applied to the induction coil to heat the powder and die. Substantial pressure (e.g., about 8,000 psi) is then applied to the die to sinter the powder material and form the gradient armor system. While the foregoing type of armor system was promising in terms of performance, the powder metallurgy process used to form the graded composite layers proved difficult to implement in practice. Consequently, such armor systems have never been produced on a large-scale basis.